20.1 Introduction

Capsular tension rings (CTRs) are designed to be placed within the capsular bag during cataract extraction and intraocular lens (IOL) implantation. Originally intended as a device to maintain capsular bag shape, the CTR has evolved into an important tool to manage weak zonules at the time of cataract surgery, enhance IOL position within the capsular bag, and prevent posterior capsule opacification (PCO).

In the late 1980s, investigators in Japan designed an endocapsular ring device for the purposes of reducing lens epithelial cell migration and preventing PCO. In 1991, Hara et al described a closed silicone ring, which they called the equator ring, to maintain the capsular bag contour. ¹ At the same time, Nagamoto and Bissen-Miyajima presented and later published on an open polymethyl methacrylate (PMMA) ring known as the capsular bag supporting ring to maintain the capsular bag contour and prevent decentration and deformation of foldable IOLs. ² Leger et al further described the CTR with rounded eyelets to ease the insertion of the device into the capsular bag. ³

Since the early developments of the device, surgeons have investigated and used the CTR for six broad indications:

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  Maintaining capsular bag shape and position in the presence of weak zonules during surgery and IOL centration postoperatively.

  
  
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  Enhancing predictability and performance of the IOL within the capsular bag with respect to effective lens position, reducing tilt and higher-order aberrations (HOAs), and reducing IOL rotation.

  
  
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  Reducing PCO.

  
  
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  Managing aniridia with iris prosthetic designs on a CTR platform.

  
  
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  Providing a platform for an intraocular pressure (IOP) sensor.

  
  
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  Providing a drug delivery platform.

Specific indications and contraindications for CTR implantation are listed in Table 20-1.

CTRs can be placed into an intact capsular bag at any time point after the creation of a continuous curvilinear capsulorhexis (CCC). As outward forces are placed on the capsule, the CTR should be avoided in the presence of an anterior capsule or posterior capsule tear due to risk of extension (Table 20-2). The presence of a discontinuous capsulotomy or an incomplete femtolaser-assisted capsulotomy may run the risk of anterior capsular tear runout. That said, if an anterior capsule or posterior capsule rent occurs after the CTR has been inserted into the bag, it is generally felt to be safe to leave it in place.

20.2 CTR Design

The current CTR design is typically made of PMMA with a round or oval-shaped cross-section, with a leading and trailing eyelet designed as a “ski ramp” to enable smooth insertion into the capsular equatorial region and allow engagement with an injector hook or instrument (Fig. 20.1). The open loop compressible design facilitates insertion through a small incision and the anterior chamber into the capsular bag. The CTR is typically distensible by ~ 2 mm from its uncompressed state to its compressed state within the capsular bag. Depending on the specific manufacturer, the CTR may vary in stiffness and spring constant. ⁴

When in the capsular bag, the outward centrifugal forces of the CTR expand the bag to provide equal circumferential force and zonular tension. This expansile force acts to centralize a capsular bag and places tension on the anterior and posterior capsule, thereby reducing capsular laxity.

Ideally, to achieve 360° of circumferential support and symmetrical zonular tension, the end terminals of the CTR should overlap. There is some variation in capsular bag sizes, which appears to correlate somewhat with corneal diameter and axial length. ⁵ Clinically, Vass et al indirectly measured capsular bag diameter, which was 10.37 mm on average, and found a positive correlation with axial length and corneal diameter, among other variables. ⁶ However, Khng and Osher did not find a correlation with corneal diameter and capsular bag size when examining cadaveric eyes. ⁷ The typical CTR size is 13 mm, which compresses to 11 mm. This is sufficient for the majority of capsular bags. Other sizes include 14.5 mm, which may be used for larger eyes (i.e., horizontal corneal diameter > 12 mm, or axial length > 27 mm), or 12 mm, which may be used for micro-ophthalmic or nanophthalmic eyes. Most experienced surgeons prefer to err on the side of choosing a larger CTR diameter to ensure adequate circumferential support. To reduce the risk of cortical entrapment behind a CTR, Henderson et al devised a scalloped ring. ⁸

20.3 CTR Implantation Technique

Insertion of the CTR must be done atraumatically to avoid entrapment of the leading eyelet in the capsular equator or traction on the capsular bag that may cause capsule rupture or zonular trauma. Insertion can be done manually or with the use of the injector. Various techniques have been described for CTR implantation and include direct dialing into the capsular bag, a fishtail insertion technique, ⁹ use of a suture in the leading eyelet, ¹⁰ or with assistance of a second instrument. ¹¹ When injecting or dialing the CTR into the capsular bag, care should be taken to ensure the leading eyelet enters the capsular bag (avoiding sulcus placement), and just under the anterior capsule at the plane of the anterior capsule to avoid posterior capsule trauma. This can also reduce the risk of cortical entrapment around the CTR.

Insertion can be performed clockwise or counterclockwise, ideally toward the area of zonular instability or dialysis. The first contact of the CTR with the capsular bag is an important step to avoid entrapment; thus the leading eyelet should enter as tangentially as possible. Thus, for a clockwise insertion, the injector should be held to the left side of the capsular bag to allow for smooth contact with the undersurface of the leading eyelet with the capsular equator. It is also helpful to avoid traction on the capsulorhexis, so, for injecting the CTR into the capsular bag, the injector hub should be placed at the capsulorhexis edge (or into the capsular bag if implanted after cataract extraction), not farther anterior into the anterior chamber (Fig. 20.2). To avoid traction on the capsulorhexis, it is advantageous to release the trailing eyelet under the anterior capsule (Fig. 20.3). CTR placement is demonstrated in Video 20.1.

There has been much debate as to ideal timing for CTR implantation. ¹² Table 20-3 summarizes the pros and cons of early versus late placement. A CTR may be placed at any time after the creation of a CCC (early), but may also be placed after phacoemulsification and cortical removal (late). It is advisable, if placing a CTR late, to do so prior to IOL implantation to prevent potential entanglement of the haptic with the CTR. The two optimal times to place a CTR are either right after CCC creation or just before IOL implantation—anytime in between increases the risk of cortical entrapment. Early insertion provides intraoperative support in the face of zonular deficiency, reducing the laxity of the posterior capsule that risks aspiration or trauma during surgery. Furthermore, early placement prevents equatorial collapse of the capsular bag, and vitreous prolapse around the capsular equator. If implanting a CTR early, it is important to avoid cortical entrapment behind the CTR, which can make cortex removal difficult. This is helped by adequate anterior viscodissection with a cohesive ophthalmic viscosurgical device (OVD) to adequately separate the cortex from the capsule and create sufficient space for the CTR to be placed in the bag (Fig. 20.4). If the cortex is trapped behind a CTR, gentle tangential stripping and/or removal of cortex above and below the device may be required. Implantation of the CTR late in the procedure is primarily for postoperative benefit only. In those cases, capsular retractors may be used for intraoperative support.